This commit adds support for GraphQL fragments with `GraphQlTester`.
Fragments allow to avoid repetition in GraphQL requests by reusing
field selection sets.
For example, the "releases" fragment can be reused in multiple queries
and make the overall document shorter:
```
query frameworkReleases {
project(slug: "spring-framework") {
name
...releases
}
}
query graphqlReleases {
project(slug: "spring-graphql") {
name
...releases
}
}
fragment releases on Project {
releases {
version
}
}
```
With this change, `GraphQlTester` accepts fragments as `String` or can
load them by their name using the configured `DocumentSource`, similarly
to the document support.
Closes gh-964
a9a8d0b745